Conventional casting moulds for the production of concrete or similar pipes in an upright position comprise outer and inner mould parts as well as a lower part or a so-called bottom ring and a locking mechanism to releasably clamp said bottom ring to the outer mould.
Vibratory movements are generally applied when using such a casting mould, and the casting mass may further during at least part of the moulding process be charged with a stationary, vertical pressure exerted through an upper mould part consisting of a profiled ring that closes the uppermost end of the annular casting cavity between the outer mould and the inner mould or core and serves to the shaping of the upwards directed end of the pipe. Especially owing to the vibratory movements the casting mass has a marked tendency to penetrate through the joint between the outer mould and the bottom ring, and the said locking mechanism serves to counteract this tendency by clamping the outer edge portion of the bottom ring firmly onto the lowermost edge of the outer mould. In a known embodiment the locking mechanism is constituted by a number of separate toggle lock devices mounted on the exterior of the outer mould part, or the outer mould, and which in their locking position engage under the outer edge portion of the bottom ring and tighten it firmly against the lower edge of the outer mould.
After the casting mass has been sufficiently vibrated the casting is removed from the mould in the way that the profiled ring, if any, is raised and then swung aside, the outer mould and the bottom ring with the newly cast tube being subsequently raised from the interior mould part or core by an upward displacement and then brought to a hardening station. At this station the toggle lock devices are released, following which the outer mould is removed from the pipe by an upward displacement and is then ready for renewed use while the newly cast pipe remains standing on the bottom ring till it has become sufficiently stable.
The known toggle lock devices are comparatively expensive as regards both manufacture and operation. Thus, they are composed of a large number of separate elements that are exposed to considerable wear, particularly by the influence of vibrations which might imply that the bottom ring shows a tendency to rotate slowly relative to the outer mould part, thereby causing a disadvantageous lateral loading on the toggle lock devices. Moreover, the locking and releasing operations of said toggle devices require considerably manual work inasmuch as large pipe diameters might necessitate the use of twelve to fourteen individual locks to obtain the necessary tightness between the bottom ring and the outer mold part. Particularly the release operation causes a further drawback, viz. that a certain clearance is required around the outer mould which prevents a close arrangement of recently cast pipes at the hardening station unless the pipes are displaced subsequent to the removal of the outer mould which, however, is troublesome and involves the risk of damage to the pipes.